Interpretive Summary: Many of the biological processes that occur in soils like decomposition of manure or contaminants like pesticides are affected by soil temperature. Decomposition of organic materials occurs faster when the soil is warmer. Knowledge of the ability of a soil to conduct heat (thermal conductivity) is useful in understanding how biological processes might vary in time or by location. A study was conducted on a fallow field in Nigeria where soil thermal conductivity and water content were measured across the field at 5 depths. The results showed that thermal conductivity and water content at adjacent locations and depths were often very different. Statistical models were used to help describe how these properties changed across the field and relate them to other soil properties. This research is important to growers trying to manage their fields to improve the recycling of organic materials and increasing soil organic matter content.

Technical Abstract:
Spatial and temporal variability studies of thermal properties were carried out on a clayey soil at Abeokuta, southwestern Nigeria. Thermal conductivity (K) was measured at 3 locations and 5 depths (0.06, 0.12, 0.18, 0.24, and 0.30 m) near each grid point using a microprocessor-based thermal property sensor. Volumetric water contents (WC) were measured using the gravimetric method at the same depths. The overall means +/- standard deviation for K and WC were 1.33 +/-0.27 W m**-1 K**-1 and 0.44+/-0.08 m**3 m**-3, respectively. A spherical model provided the best fit to the isotropic variograms of WC in all the layers while for K, spherical, linear, and exponential models were observed with nugget-to-sill ratios < 1.0 and effective ranges from 92 to 571 m. Results indicate an inconsistent spatial pattern of K with spatial correlations that vary by parameter and depth.